Cathode ray tube circuit



Oct. 17, 19,44. J B, MAGGIQ 253605356 CATHODE RAY TUBE CIRCUIT Filed June 25, 1942 CA THODE FIG RAY DEV/CE HODUL A TING AMP.

.4400. I ,7 INPUT CA 77100: RAY DEV/CE y F/ 6. Z

MODULA T/NG 7 MR H B\ /2 9 15 /5 /N l E N TOR J. B. MAGG/O BY imw aw ATTORNEY i Yatented Get. 17, 1944 CATHODE RAY TUBE CIRCUIT John B. Maggio, Summit, N. .l., assignor to Bell Telephone Laboratories,

Incorporated, New

York. N. Y.. a corporation of New York Application June 25, 1942, Serial No. 448,429

6 Claims.

This invention relates to cathode ray devices and more particularly to beam control circuits therefor.

In cathode ray devices and in particular those devices wherein deflection of the beam is produced by electrostatic means it is necessary to maintain the deflecting plates at the same direct' current potential as the accelerating electrode. To ease the requirements for the deflecting amplifler circuit it has been the customary practice to operate both the accelerating electrode and the deflecting electrodes at direct current ground potential. This makes it necessary to operate the cathode and the other control electrodes comprising the electron gun at a relatively high negative potential. To successfully do this for circuits where a beam intensity modulatoris used it has been necessary to have thepower supply closely regulated to prevent fluctuations in power supply voltage. Such variations modulate the beam by reason of the fact that the beam intensity control electrode or grid is often coupled to ground through a relatively low impedance path so that the power supply variations are impressed efiectively between the cathode and the beam control electrode. In many systems power supply voltage variations of only two per-cent will completely modulate the spot intensity. Where cathode ray devices are to be operated at a plurality of different voltages or where it is desired to dispense with closely regulated high voltage power supply systems, it is necessary to arrange the cathode ray circuit so that it is substantially insensitive to these power supply variations.

It is the object of this invention to provide a circuit for the electron gun of a cathode ray device which is substantially insensitive to voltage variations of the power supply. circuit.

The foregoing object is attained by this invention which provides a circuit comprising an alternating current bridge having two pairs of terminals, the direct current power supply being connected to one pair of said terminals, the accelerating electrode being connected to the bridge terminal which is connected to the positive pole of the power supply, and the cathode and beam intensity control electrode being connected to the other pair of bridge terminals.

The invention may be better understood by referring to the accompanying drawing in which:

Fig. l is a circuit typical of many cathode ray devices of the prior art;

Fig. 2-discloses the circuit of Fig. 1 modified to embody this invention;

Fig. 3 is a circuit showing in conventional .bridge form the part of Fig. 2 embodying this invention; and

Fig. 4 is a circuit showing only those elements of Fig. 3 which are active in forming the balanced bridge structure.

Referring now more particularly to Fig. 1 it will be noted that the cathode ray device I includes as parts thereof an accelerating electrode II, a positive control electrode I2, a negative beam intensity control electrode I3 and a cathode I4, these elements comprising an assembly commonly called an electron gun. Additional elements, not shown, are also supplied in a variety of forms well known to the art and depending upon the specific use to which the device is to be put.

In order to control the beam intensity a modulating amplifier 2. may be provided having an output resistor 3. The alternating current component developed across resistor 3 is applied to beam intensity control electrode I3 of cathode ray device I through a coupling condenser 5. Normal direct current bias of electrode I3 is provided through resistor 6 from potentiometer I and may be adjusted by moving slider I. Suitable voltages are applied to the other electrodes of cathode ray device I through a voltage divider network comprising resistors I, 8 and 9, the source of this voltage coming from a direct current supply I1. A filter condenser I5 is connected across the divider network as shown.

The accelerating electrode II must be positive with respect to cathode I4 and as it is customarily the most positive of all the electrodes, it is connected to the positive pole of source H. In order to maintain the accelerating electrode I I at ground potential, the positive end of source I1 is grounded at I6.

For most cathode ray devices it is necessary to maintain a potential difference of several thousand volts between accelerating electrode I l and cathode I4. The impedance of the path from electrode I3 through condenser 5, resistor 3, condenser 4 to ground I8 is relatively low. This low impedance path from control electrode I3 to ground'efiectively maintains this electrode at ground potential in so far as fluctuations in the supply voltage are concerned. However, since the potential of the cathode I4 will fluctuate with respect to ground as the supply voltage varies, these variations in supply voltage will appear between the grid I3 and cathode I4.

resistance l9 and a condenser of relatively large capacity!!! have been inserted in the bias circuit for beam control electrode it. Also the lower end of filter condenser I! has been connected directly to cathode ll rather than to the lower end of bias control potentiometer I. It will be observed that these changes have transformed the circuit into the form of an alternating current bridge having one pair of terminals X, Y to which the power supply I1 is connected and another pair of terminals A, B to which are connected cathode l4 and beam control electrode l3, respectively. When this bridge network is properly balanced fluctuations in voltage from power supply ll being impressed-on terminals X, Y will have no effect on the voltage applied to beam control electrode i3 with respect to cathode I4 since these latter two electrodes are connected across the other pair of bridge terminals.

To better understand the circuit of Fig. 2 it has been redrawn in conventional bridge form in Fig. 3. In thisfigure terminals X, Y and A, B are as shown in Fig. 2. Also thevarious elements of cathode ray device I, grounds it and I8 and power supply source II bear the same reference niunerals as in Fig. 2. The various subscript numerals for the variou. resistors and'condensers in the bridge network correspond with the similarly numbered elements in Fig. 2. For example, resistor in Fig. 2 is denoted R in Fig. 3. This bridge network is balanced when the following equation is satisfied:

Race =R1C15 (1) .It will be readily understood that this is so when it is remembered that the impedance of condenser 20 is small compared with the resistance slider I will still provide the desired adjustments of the direct current bias of beam control grid Hi. It will also be evident that voltage variation appearing across resistor 3 -will be effectively impressed between cathode l4 and beam control grid I3 through series-connected condensers 4, 5 and I! represented in Fig'. 3 by capacities C4, C5 and C15.

Fig. 4 shows the invention stripped of all of the impedance elements which have no appreciable effect on the balanced condition of the network. It will be seen that the alternating current bridge is made up a simple network of It will be obvious to those skilled in the art that when the impedance elements have been so selected as to cause this bridge to be balanced that it will be balanced for all frequencies and that fluctuations in supply'voltage impressed on terminals X, Y will not appear across terminals A, B.

What is claimed is:

1. In a circuit for stabilizing the beam intensity of a cathode ray device with respectI to variations of the direct current power supply voltage, said device having an electron gun including as parts thereof accelerating and beam intensity electrodes and a cathode, the circuit comprising a four-terminal alternating current bridge balanced at substantially all frequencies, two of said terminals providing connections for the direct current power supply, and connections for connecting the cathode and the beam intensity electrode respectively to the remaining two terminals, whereby variations in the voltage of the direct current supply do not afiect the voltage between said cathode and said beam intensity electrode.

2. In a circuit for stabilizing the beam intensity of a cathode ray device with respect to variations of the direct current power supply voltage, said device having an electron gun ineluding as parts thereof accelerating and beam intensity electrodes and a cathode, the circuit comprising a four-terminal alternating current bridge balanced at substantially 'all frequencies, two of said terminals providing connections for the direct current power supply, a connection from the accelerating electrode to the bridge terminal which .is connected to the positive pole of the power supply, and connections for connecting the cathode and the beam intensity electrode, respectively, to the remaining two terminals, whereby variations in the voltage of the direct current supply do not affect the voltage between said cathode and said beam intensity electrode.

3. In a circuit for stabilizing the beam intensity of a cathode ray device with respect to variations .of the direct current power supply voltage, said device'having an electron gun including as parts thereof accelerating and beam intensity electrodes and a cathode, the circuit comprising a four-terminal alternating current bridge having impedance elements balanced at substantially all frequencies, two of said terminals providing connections for the direct current power supply, connections for connecting the cathode and the beam intensity electrode respectively to\the remaining two terminals, a direct. current path from said cathode to said beam intensity electrode including a potentiometer for adjusting the direct current'bias of said beam intensity electrode, said path also-including aresistor shunting some of said bridge impedance elements the resistance whereof ishigh compared to the impedance of the bridge elements shunted thereby, whereby variations in the voltage of the direct current supply do not afiect the voltage between the cathode and said beam intensity electrode. 5 I v 4. In a circuit for stabilizing the beam intensity of a cathode ray device with respect to variations of the direct current power supply voltage, said device having an electron gun including as parts thereof accelerating and beam intensity electrodes and a cathode, the circuit comprising a four-terresistances R0 and R1 and capacities Cs and Cu. ll

minal alternating currentbridge having impedance elements balanced at substantially all frequencies, two of said terminals providing conncctions for the direct current power supply, a connection from the accelerating electrode to the bridge terminal which is connected to the positive pole of the power supply, connections for connecting the cathode and the beam intensity electrode respectively to the remaining two ter minals, a direct current path from said cathode to said beam intensity electrode including a potentiometer for adjusting the direct current bias of said beam intensity electrode, said path also including a resistor shunting some of said bridge impedance elements the resistance whereof is high compared to the impedance of the bridge elements shunted thereby, whereb variations in the voltage of the direct current supply do not affect the voltage between said cathode and said beam intensity electrode.

5. In a circuit for stabilizing the beam intensity of a cathode ray device with respect to variations of the direct current power supply voltage, said device having an electron gun including as parts thereof accelerating and beam intensity electrodes and a cathode, the circuit comprising a four-terminal alternating current bridge having impedance elements balanced at substantially all frequencies, a plurality of branches including said impedance elements interconnecting said four terminals, two of said terminals providing connections for the direct current power supply, connections for connecting the cathode and the beam intensity electrode respectively to the remaining two terminals, modulating means for varying the vol age across at least one of the impedance elements in one oi said branches to correspondingly vary the voltage between said cathode and said beam intensity electrodes. 5 whereby variations in the voltage of the direct current supply do not affect the voltage between said cathode and said beam intensity electrodes. 6. In a circuit for stabilizing the beam intensity of a cathode ray device with respect to variations of the direct current power supply voltage, said device having an electron gun including as parts thereof accelerating and beam intensity electrodes and a cathode, the circuit comprising a four-terminal alternating current bridge having impedance elements balanced at substantially all frequencies, a plurality of branches for said bridge including said impedance elements interconnecting said four terminals, two of said terminals providing connections for the direct ourrent power supply, a connection from the accelerating electrode to the bridge terminal which is connected to the positive pole of the power supply, connections for connecting the cathode and the beam intensity electrode respectively to the remaining two terminals, modulating means for varying the voltage across at least one of the impedance elements in one of said branches to correspondingly vary the voltage between said cathode and said beam intensity electrodes, whereby variations in the voltage of the direct current supply do not afiect the voltage between said cathode and said beam intensity electrodes.

JOHN B. MAGGIO. 

